diff --git a/deepinfer/environ.py b/deepinfer/environ.py
index 332064a..e3a55bb 100644
--- a/deepinfer/environ.py
+++ b/deepinfer/environ.py
@@ -7,10 +7,17 @@ from datetime import timedelta
 from typing import Any
 
 DEFAULT_PREFILL_MAX_SUM_SEQLEN_K = 2**30
+_FALSE = {"0", "", "false"}
+_TRUE = {"1", "true"}
 
 
 def _bool(v: str | None, default: str = "0") -> bool:
-    return (v if v is not None else default) not in ("0", "", "false", "False")
+    value = (v if v is not None else default).lower()
+    if value in _FALSE:
+        return False
+    if value in _TRUE:
+        return True
+    raise ValueError("expected one of '0', '1', 'false', 'true' (case-insensitive)")
 
 
 def _int(v: str | None, default: int = 0) -> int: